1. Field of the Invention
The present invention relates to an image forming apparatus.
2. Description of the Related Art
Related art color image forming apparatus employing an electrophotographic recording method, such as laser printers, copiers, and facsimile machines, are known to use an intermediate transfer member configuration. As a primary transfer process, a toner image formed on a photosensitive drum (image bearing member) is transferred onto an intermediate transfer belt (intermediate transfer member). By running this process at image forming stations corresponding to yellow (Y), magenta (M), cyan (C), and black (Bk), multiple color toner images are formed on a surface of the intermediate transfer belt. As a secondary transfer process, the multiple color toner images formed on the surface of the intermediate transfer belt are then transferred together onto a surface of a recording material such as paper. By then using a fixing unit to permanently fix the toner images transferred together to the surface of the recording material, a color image is formed on the recording material.
Japanese Patent Application Laid-Open No. 2012-137733 proposes a configuration that combines primary transfer and secondary transfer by making current flow from a secondary transfer portion in a peripheral direction of an intermediate transfer belt in order to reduce power supply costs in an image forming apparatus having the configuration described above.
In order to prevent transfer failure and to reduce the cost, the configuration disclosed in Japanese Patent Application Laid-Open No. 2012-137733 performs primary transfer by employing an intermediate transfer belt as an intermediate transfer member, connecting a secondary transfer voltage power supply (high voltage power supply) to a driving roller that stretches and moves the intermediate transfer belt, and causing current to flow in the peripheral direction of the intermediate transfer belt.
In contrast, Japanese Patent Application Laid-Open No. 2009-205012 proposes a method of intermediate transfer belt cleaning where, in order to clean the intermediate transfer belt following a secondary transfer process, secondary transfer toner remaining on the intermediate transfer belt is uniformly charged by a charging member contacting the intermediate transfer belt to collect the secondary transfer toner by a photosensitive drum of a primary transfer portion.
With the configuration of Japanese Patent Application Laid-Open No. 2012-137733, there is a risk that the polarity of a primary transfer portion may change in response to the polarity of current supplied from a member contacting the intermediate transfer belt. For example, if intermediate transfer belt cleaning is performed using a charging member, the polarity of the primary transfer portion may not be able to maintain a desired polarity, and it may be difficult to collect toner from the intermediate transfer belt to the photosensitive drum in the primary transfer portion.